Doggie taking on 100 enemies after morphing for the first time. There's even a counter. If ever there was one; the Law of Conservation of Ninjutsu was in full force for that fight.
Not only that but he does so in 2 minutes.
In the first episode, during the training simulation, it's Boom who takes on THREE of the rangers (unmorphed) as the simulated Monster of the Week. Kind of sucks that he never ascended, considering how Badass that was.
Even though she didn't actually win, Sophie, the girl of the week in "Wired," may have had the series Crowning Moment Of Awesome with her fight against the villain who was after her. It was one of the most competent fights in the series in terms of choreography, execution, and showmanship, all with a character who was the episode's victim, and who was the target of a great deal of speciesism earlier in the episode.
Two words: "I'm staying."
In addition, Boom doesn't even dispute the situation, but still manages to come off as one of his shining moments in rallying the misfits to fight on regardless of the situation.
Sky assuming the Red Ranger powers — and the newly created Battlizer — to take down Mirloc, an escaped criminal who killed his father.
Kat's one-shot morph, as well as the fight with the Mooks before it. Then she stops the rigged enemy mecha from exploding while the others are fighting it.
The fact that this is the first Power Rangers series to have a female Red Ranger. Made better by how Bruce Kalish fought Disney in order to have a female Red Ranger in the first place. Sadly she's evil but it's still a nice thing to have.
Also the fact that this was before Shinkenger- Power Rangers had a Female Red about four years before Super Sentai.
The Rangers defeating A-Squad. As Linkara noted in History of Power Rangers, throughout the series B-Squad suffered from a lot of Always Someone Better due to standing in A-Squad's shadow, so for them to once and for all prove themselves by surpassing their predecessors was awesome.
Also in the finale, Doggy capturing Mora. She keeps sketching monsters and throwing them at him, but he destroys each one with a single blow of his sword, until she finally runs out of pages in her sketchbook. It even comes with a Bond One-Liner:
Doggy: Use your imagination.
Cruger got an even better line in towards Gruumm after that.
"Now they match."
The fact that in the last episode, Jack flat-out quits to help the homeless versus staying on as a Ranger because he feels it'll be more helpful. No one had ever walked away from being a Ranger like that, and unlike Jason, Trini and Zack going to the Peace Conference, this wasn't the result of Executive Meddling; by all accounts, Brandon Jay Mc Laren has a good relationship with the show.